The dynamics of yo-yo motion are considered in this article. Many textbooks have examined the "rolling" motion of a yo-yo as it moves vertically up or down. However, in the vicinity of the lowest point, a jerk in the string occurs as the center of mass transitions from a linear motion to a pure rotational motion (with respect to the end of the thread). String tension at the lowest point is calculated, and it is established that it is usually much greater than tension when the yo-yo moves up or down. Experimental data are in agreement with theoretical predictions.